The concept of routing interrupt lines to an irqchip is nothing
that is IOAPIC specific. Every irqchip has a maximum number of pins
that can be linked to irq lines.

So let's add a new define that allows us to reuse generic code for
non-IOAPIC platforms.
Signed-off-by: NAlexander Graf <agraf@suse.de>
Acked-by: NMichael S. Tsirkin <mst@redhat.com>